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June 19, 2012 -- Apples again have the dubious honor of nabbing the top spot on the ''Dirty Dozen'' list of produce with unacceptable pesticide residues, issued by the Environmental Working Group.

EWG has also issued its updated "Clean Fifteen" list of produce least likely to be tainted with pesticides.

For the first time, the group also tested prepared baby food consisting of green beans, pears, and sweet potatoes. Its evaluation shows that some green bean and pear samples had pesticide residues, while sweet potatoes had virtually no detectable residues.

"Our advice to consumers is to choose the organic version of the fruits and vegetables on the dirty dozen list," Johanna Congleton, PhD, MSPH, an EWG senior scientist, tells WebMD.

While EWG scientists prefer organic versions of some produce, they do concede that ''eating commercially grown produce is better than not eating fruits and vegetables at all."

Another expert not involved in the report has some criticisms. "Their rankings are just very arbitrary," says Carl K. Winter, PhD, director of the FoodSafe program and an extension food toxicologist at the University of California, Davis.

He reviewed the findings for WebMD. "I think consumers should eat lots of fruits and vegetables, whether organic or conventional," Winter says, and there is no reason to fear these foods.

Dirty Dozen, 2012 Version

Besides apples, 11 other fruits and vegetables -- in order of the amount of pesticide residues, from more to less -- earned a spot on the Dirty Dozen list:

Celery

Sweet bell peppers

Peaches

Strawberries

Nectarines (imported)

Grapes

Spinach

Lettuce

Cucumbers

Blueberries (domestic)

Potatoes

This year, EWG scientists added a "Plus" category to highlight two crops -- green beans and leafy greens such as kale and collard greens. They did not meet the criteria typically used for the Dirty Dozen list but were commonly contaminated with highly toxic organophosphate insecticides.

These insecticides, Congleton tells WebMD, are toxic to the nervous system. They have largely been removed from agriculture over the past decade. But they are not banned, so they still sometimes show up on crops.

According to EWG, pesticide exposure is linked with a range of other health problems, including hormone disruption, cancer, brain toxicity, and skin, eye, and lung irritation.

Clean Fifteen, 2012 Version

Making the updated "Clean Fifteen" list because they were found to be lowest in pesticides are:

Onions

Sweet corn

Pineapples

Avocado

Cabbage

Sweet peas

Asparagus

Mangoes

Eggplant

Kiwi

Cantaloupe (domestic)

Sweet potatoes

Grapefruit

Watermelon

Mushrooms

Produce & Pesticides: Baby Foods

In the baby food evaluation, green beans tested positive for five pesticides. The evaluation of pears found 92% positive for at least one pesticide residue.

Sweet potatoes came up cleanest.

Making the Lists: Methods

The EWG has issued the lists for the past eight years. EWG scientists used pesticide testing data generated by USDA and FDA scientists to create the lists. In most studies, produce was tested after it was washed or peeled.

"Contamination was measured in six different ways," says Alex Formuzis, an EWG spokesman.

These include:

Percent of samples tested with detectable pesticides

Percent of samples with two or more detectable pesticides

Average number of pesticides found on a single sample

Average amount (in parts per million) of all pesticides found

Maximum number of pesticides found on a single sample

Total number of pesticides found across all samples of the same produce type

"The foods on the dirty dozen list contained the highest amount of pesticides," Congleton says.

Regarding the Clean Fifteen list, she says, "Some of them do have detectable levels of pesticides. However, they are the lowest out of all the foods we evaluated. Some had undetectable levels of pesticides."

Produce and Pesticides: Another View

Winter of UC Davis explains why he says the lists are arbitrary. "What they are not doing is addressing the three important components that scientists have to use to establish whether there is any risk," he says.

The three components include the amount of pesticide, how much is consumed, and how toxic it is.

Winter concludes that "the average amount of exposure is negligible."

"Consumers should not fear conventionally produced fruits and vegetables," he says. "The levels of residues are at levels so low there should not be concern."

Winter says he gets no funding from chemical, agricultural, or food industries.